Typically, a radio communication link between two radio transceivers is limited by a distance between the two radio transceivers. In particular, radio-link characteristics, for example, such as a quality and a bandwidth of the radio communication link typically degrade as a function of the distance between the two radio transceivers.
In free air, the radio-link characteristics can be predicted in a straight forward manner using propagation models. However, in situations where the radio communication link between the two radio transceivers is obstructed by objects, such as buildings, terrains, forests and the like, the quality of the radio communication link suffers.
FIG. 1 is a schematic illustration of an example environment; FIG. 1 represents prior art. In FIG. 1, there is shown a ground station 102 and an associated antenna 104. The ground station 102 and the antenna 104 are installed at a geographical position that is surrounded by a city infrastructure, such as buildings, and a ground with varying altitude, such as a mountainous terrain.
In the example environment, three airborne measurement devices, namely an airborne measurement device 106a, an airborne measurement device 106b and an airborne measurement device 106c, are employed to collect measurement data. The airborne measurement device 106a, the airborne measurement device 106b and the airborne measurement device 106c are hereinafter referred to as airborne measurement devices 106.
The ground station 102 sends control instructions to the airborne measurement devices 106. Such communication between the ground station 102 and the airborne measurement devices 106 is typically arranged via a direct radio communication link between the ground station 102 and the airborne measurement devices 106.
Problems arise when there is no direct line-of-sight between the ground station 102 and the airborne measurement devices 106. As an example, the airborne measurement device 106a is occluded by the city infrastructure, while the airborne measurement device 106b is occluded by a higher terrain point. Moreover, the airborne measurement device 106c is occluded by the curvature of the Earth. Such occlusion substantially attenuates a signal strength of the radio communication link, thereby degrading the quality of the radio communication link.
A conventional technique for overcoming the aforementioned problems employs directional antennae for better amplification of radio signals. Another conventional technique employs tracking antennae for higher amplification of radio signals. Yet another conventional technique employs a higher antenna tower.
However, these conventional techniques suffer from several disadvantages. Firstly, antennae employed in these techniques are large in size and heavy in weight. Deployment and withdrawal of such large-sized and heavy antennae is time-consuming and costly. Secondly, mobile antennae are typically limited to a certain height, which, in turn, limits a maximum transmission and/or reception distance of the mobile antennae to only a few kilometers. This restricts a range of flight operations of airborne measurement devices receiving control instructions from a ground station via a mobile antenna, thereby requiring frequent relocations of the ground station and the mobile antenna. In case of an emergency, such as disaster management, such antenna may be simply too slow to deploy.